1. Field of the Invention
The present invention relates to a new electric light bulb and a new coating method for an electric light bulb. In particular, it relates to technology that lengthens the lifetime of an electric light bulb. The color temperature of radiated light of the light bulb is raised by the coating, the number of light fluxes are increased, and the electric light bulb is readily manufactured.
2. Description of the Related Art
Halogen lamp light sources have been used as automobile headlamps for a long time. More recently, a discharge lamp has been used as the light source of the headlamp.
However, halogen lamps are still in use, and users of the halogen lamp hope that the color temperature of the halogen lamp, which is about 2800 K, can be brought closer to the color temperature of the discharge lamp, which is about 4000 K.
One method of raising the color temperature is to increase the power supplied to the halogen lamp. However, this method reduces the lifetime of the electric light bulb. Therefore, in order to raise the color temperature, an attempt to remove a red component from the radiated light has been made by alternately laminating an evaporation film of titanium dioxide (TiO2) and an evaporation film of silica (SiO2) in eight to ten layers and then reflecting the red component at a boundary of each layer. However, according to this method, in an electric light bulb having a filament that is not positioned in the center of the bulb (for example, a high beam filament in a H4 bulb including a filament for high beam and a filament for low beam), a red component of light radiated from the filament and reflected at the layer boundary of the above evaporation films is projected at positions symmetrical with respect to the filament, so that a problem occurs because the red light is radiated onto the lower portion of the luminous intensity distribution of the high beam.
Therefore, four to eight layers of blue coating films have been formed on the glass bulb, so that the color temperature of the halogen lamp could be increased to about 3600 to 3700 K. Since the red component of the radiated light is absorbed in the blue coating films, the red light is prevented from leaking out on the lower portion of the luminous intensity distribution, in contrast to the electric light bulb of the previous example having the above described laminated evaporation films.
Generally, a light source bulb used in a headlamp for an automobile is subjected to a shield coating at the leading end thereof in order to prevent direct rays from being radiated. Conventionally, a shield coating was applied by using black paint. FIG. 7 illustrates a conventional electric light bulb xe2x80x9caxe2x80x9d subjected to the above blue coating, and the black coating xe2x80x9ccxe2x80x9d was applied onto a blue shield coating xe2x80x9cbxe2x80x9d. The conventional electric light bulb having a black coating c absorbs heat of the radiated light, so that the heat builds up within the leading end portion. Such a bulb has a problem because the blue coating tends to peel as the electric light bulb a is used repeatedly.
Further, since the black coating c also absorbs the radiated light, there is also a problem that the absolute number of the number of light fluxes is reduced, in cooperation with the light absorbed by the coating b.
The invention provides an electric light bulb which prevents peeling of the coating and suppresses reduction of the number of light fluxes. In addition, such an electric light bulb is easy to manufacture.
The electric light bulb of the invention includes a blue coating applied onto a straight portion of the tube, and a white or silver shield coating applied onto a leading end portion that is continuous with the straight tube. According to the electric light bulb of the invention, since the white or silver shield coating reflects heat and light without absorbing them, peeling of the coating caused by heat build-up within the leading end portion subjected to the shield coating does not occur, and the light reflected by the shield coating can be utilized effectively. Therefore, a reduction of the number of light fluxes can be suppressed.
A coating method of an electric light bulb according to the invention includes dipping the straight tube portion and the leading end portion that is continuous with the straight tube into color paint to apply the color paint onto them. Next, the leading end portion is dipped into a diluent of the color paint to remove the color paint applied onto the leading end portion. Lastly, the leading end portion is dipped into white or silver shield paint to apply the shield paint onto the leading end portion.
According to an implementation of the coating method of the electric light bulb of the invention, the straight tube portion of the electric bulb is subjected to only the blue coating and the leading end portion is subjected to only the shield coating. Such an electric light bulb can be readily manufactured.